Since first appearing as calculator displays, liquid crystal display elements have kept pace with the development of computers, with the demand for increased display size, which was unable to be achieved by TN (Twisted Nematic) mode displays, being met by STN (Supertwisted Nematic) mode displays, and liquid crystal displays are now widely used as the interface between computers and people. Furthermore, active matrix liquid crystal display elements (AM-LCD) in which each pixel is provided with a thin film transistor are able to match the high image quality of CRT displays, and with the additional advantages offered in terms of flatness of the display and reduced energy consumption, they are considered as the displays of the future.
In recent years the demand for portable notebook type computers has increased, and so particularly for the STN-LCD and AM-LCD displays used for such applications, there has also been a demand for displays with characteristics capable of withstanding outdoor use. As a result, characteristics which have been actively sought include a superior contrast at high temperatures, the absence of crystal precipitation or smectic phase formation even at low temperatures, and no deterioration in contrast or display quality even on prolonged exposure to UV light or sunlight. However, conventional liquid crystal compounds and liquid crystal compositions have not always been able to satisfy such demands. The problem of crystal precipitation at low temperatures is particularly serious, and the only way in which to prevent such precipitation is to reduce the amount of liquid crystal compound added, but even materials with superior characteristics are often susceptible to this precipitation problem, and with the conventional, widely used unfused ring type liquid crystal compounds, this remains the most difficult problem to resolve. In other words, amongst unfused ring type liquid crystal compounds, no compound was able to simultaneously satisfy the requirements of a low crystal (or smectic) transition temperature, a high nematic-isotropic transition temperature, a high dielectric anisotropy, and a favorable elastic constant and birefringence.